Various forms of packaging, particularly for food products such as meat and poultry, employ a relatively rigid support member, such as a flat sheet or tray, upon or in which a product is supported. The product is typically covered by a relatively flexible, transparent film. The film is bonded to the support member around the product, generally by forming a heat-seal between the film and support member, to thereby enclose the product between the film and support member. Examples of this type of packaging include vacuum skin packaging and modified-atmosphere packaging.
In vacuum skin packaging, the film is thermoformable, i.e., capable of being formed into a desired shape upon the application of heat, and is thermoformed about the product on a support member by means of heat and differential pressure. Virtually all of the air is evacuated from the interior of the package so that the film conforms very closely to the contour of the packaged product. Generally, sufficient heat is applied to cause the film to bond with the support member outside the periphery of the product, either by employing a heat-activatable adhesive at the interface of the film and support member or by forming the film and support member from materials that are otherwise sealingly compatible upon the application of heat, e.g., by employing similar polymeric materials, such as polyethylenes, at the seal interface that bond to one another when heated. Alternatively, a pressure-sensitive adhesive can be used. Further details are described in, e.g., U.S. Pat. No. Re 30,009 (Purdue et al.), U.S. Pat. No. 5,346,735 (Logan et al.), and U.S. Pat. No. 5,770,287 (Miranda et al.), the disclosures of which are hereby incorporated, in their entireties, by reference thereto.
In modified-atmosphere packaging, a food product is generally packaged in a tray-like support member having a peripheral flange to which the film is secured. Prior to securing the film to the support member, air is generally evacuated from the interior of the support member and replaced by a gas which extends the shelf-life of the packaged product.
In these and similar types of packaging applications, both the film and support member generally comprise materials which form a barrier to the passage of gas therethrough so that the package is, at least initially, substantially gas-impermeable. Eventually, a portion of the film is removed by a retailer prior to placing the package in a display case for consumer purchase. The latter event occurs where it is desirable to increase the gas-permeability of the film in order to allow air (particularly oxygen) to come into contact with the packaged product while still providing protection to the product from dirt, dust, moisture, and other contaminates. This is generally desirable where air-contact with the packaged product renders the product more appealing to the consumer in some way.
While a low-oxygen packaging environment generally increases the shelf-life of a packaged fresh red meat product (relative to meat products packaged in an environment having a higher oxygen content), red meat has a tendency to assume a purple color when packaged in the absence of oxygen or in an environment having a very low oxygen concentration, i.e., below about 5% oxygen. Such a purple color is undesirable to most consumers, and marketing efforts to teach the consumer about the acceptability of the purple color have been largely ineffective. When meat is exposed to a sufficiently high concentration of oxygen, e.g., as found in air, it assumes a bright red color which most consumers associate with freshness. After 1 to 3 days of such exposure, however, meat assumes a brown color which, like the purple color, is undesirable to most consumers (and indicates that the meat is beginning to spoil). Thus, in order to effectively butcher and package fresh red meat products in a central facility for distribution to retail outlets, the meat is packaged, shipped, and stored in a low-oxygen (vacuum or modified-atmosphere) environment for extended shelf-life, and then displayed for consumer sale in a relatively high-oxygen environment such that the meat is caused to “bloom” into a red color just before being placed in a retail display case.
The foregoing may be accomplished by providing a film that peelably delaminates into a gas-permeable portion and a substantially gas-impermeable portion, with the gas-permeable portion being bonded to the support member so that the gas-impermeable portion can be peelably removed from the package. In this manner, the package may be shipped with the upper, gas-impermeable portion secured to the lower, gas-permeable portion to maintain a low-oxygen environment within the package during shipping. Then, the gas-impermeable portion may be peelably removed at the supermarket just prior to placing the package in a retail display case. Since the remaining portion of the film is permeable to gas (oxygen), it allows the meat product to bloom in the presence of oxygen which enters the package from the ambient atmosphere. This general packaging concept is also applicable to poultry, which assumes a pink color in the presence of oxygen but has a longer shelf-life in a low-oxygen environment, as well as to other perishable foods such as cheese and produce.
Regardless of the particular type of peelable package that is employed, e.g., a vacuum skin package or modified-atmosphere package, in the packaging of some products it is desirable to provide the package with an absorbent pad to soak up juices exuded by the food product. This is particularly true for the packaging of beef, lamb, poultry, and pork. The presence of free juice within the package produces an undesirable appearance to consumers, and can provide an environment for bacteriological growth within the package. It is preferred that the absorbent pad is positioned under the meat product, out of the consumer's line of sight.
During the preparation of a case-ready package of either the vacuum skin package type or the modified atmosphere type, it is desirable to rapidly evacuate the atmosphere from around the food product, tray member, and absorbent pad between the food product and the tray member. The evacuation occurs before adhering the covering film (i.e., lid film) over the tray. It has been found that the desired rapid evacuation of the atmosphere during the packaging process can cause a rupturing of the seal around an absorbent pad which has an absorbent layer enveloped by upper and lower films affixed to one another around the periphery of the pad. During evacuation, the atmosphere within the pad may not escape from the pad rapidly enough to prevent a rupture of the envelope. If the envelope ruptures, the absorbent material making up the pad may escape and adhere to the meat product, producing an appearance which is undesirable to consumers. It would be desirable to provide a pad having the absorbent layer enveloped by upper and lower webs affixed to one another around the perimeter of the pad, with the pad being able to withstand sudden evacuation of atmosphere therefrom without rupture.